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Port 80 in use on Windows 10 computer: 
You can find used port from Windows Firewall.
Click Start > Settings > Netwok and Internet > Windows Firewall
In the left pane, click Advanced Settings
In Windows Firewall with Advanced Security, click Inbound Rules.
Find Local Port 80 with Protocol TCP. in my case is "World Wide Web Services (HTTP Traffic-In)"
Once you find it, stop or disable that rule from Windows Services (World Wide Web Publishing Service).
if needed restart your pc.

Windows 10 runs IIS (Internet Information Services, Microsoft's web server software) automatically during Startup on Port 80. In order to use Apache Server on that port, IIS must be stopped.
paaacman's response refers to the IIS server as "W3SVC", or the "World Wide Web Publishing Service". I suppose that's because Windows 10 runs IIS as a service. In order to disable it or modify how the service runs, you need to know where to find "Services" in your system.
I found the easiest way there was to click on the search button next to the start menu button in the Windows 10 taskbar and type "Administrative Tools". You can either hit return or click on the "Administrative Tools" link that Windows finds for you.
A control panel window will open with a list of tools. The one you want is "Services." Double-click it.
Another window will open called "Services." Locate the one named "World Wide Web Publishing Service." Some other users in this thread have listed what it is called in other languages, if your list is not in English.
If you only want to turn off the IIS server for this Windows session, but want it to run automatically again the next time you start up Windows, right-click "World Wide Web Publishing Service" and choose "Stop." The server will stop, and Port 80 will be freed up for Apache (or whatever else you want to use it for).
If you want to prevent the IIS server from running automatically when you start up Windows in the future, right-click "World Wide Web Publishing Serivce" and select "Properties." In the window that appears, locate the "Startup type" dropdown, and set it "Manual." Click "Apply" or "OK" to save your changes. You should be all set.